Electric lighting.



C. P. STEINMETZ.

ELECTRIC LIGHTING.

APPLIOATION Hmm 1211.30. .1900.

Patented 0@t.17,1911.

UNITED sTATEs PATENT oEEicE.

CHARLES P.'sT E1NME'rz, OE SCHENECTADY, NEW YORK, v.lissiefiron ToGENERAL ELECTRIC COMPANY, A CORPORATION OP NEW YORK.

ELECTRIC LIGHTING.

Speclcation of Letters Patent. Patented 0013.17, 1911..v

Application med April 30, 1900. Serial No. 14,790.

To all whom it may concern: v

lle it known that I, CHAnLEs P. STEIN METZ, a citizen of the vUnit-edStates, residing at Schenectady, county of Schenectady, State of NewYork, have invented certain new and useful Improvements in ElectricLighting, of which lthe following is a specitication. i

I have discovered that the light from an electric arc, excluding thatportion of the light which comes directly from the crater,

. is to a, very large extent independent of the temperature at which thearc may exist, but depends rather on the nature of the substancesconstituting the are stream.. 'lhis being the case, it is advantageousto cause the arc to spring from a terminal, or between terminals,capable of giving forth vapor at eoniparativoly low temperatures, since.the temperaturo'of thearc stream is tixed, as is the temperature of anyother saturated vapor, by the boiling point of' the substance vaporized.These considerations point to the advisability of replacing the fewsubstances have their correct color` carbon arc of commerce by an arefrom terminals one at least of which is formed of lines, so that inY thelight from a mercury.

arc redl substances appear black, and very values. In a formerapplicationfor Letters Patent ot the United States, Serial Number 7 265,I have set forth and claimed a method of overcoming this very seriousdefect, and without attempting herein to define the scope of the saidapplication, or to setfortli in detail the disclosure made therein, itmay be sufficient here to state that the said application contemplatedthe addition to the arc of conducting vapors of such a nature as toreinforce the spectrum. I find that nonconducting vapors have no effectin the mercury arc, from which I am led to believe that the action isinthe nature of a sympathetic vibration of conducting vapors under` theelectrical and physical conditions existent in the arc stream. Anysubstances added tothe stream, if capable of producing conductingvapors, give light corresponding to the arc spectra of such substances,but carbon on the one hand and gases on the ,other hand, if added to thearc stream, ap-

parently have no etlect whatever, which is probably due to the extremelylow tempera-` ture at which thel mercury are is maintained.v

I have also shown in the application above set forth, that it is,commercially speaking, essential to surround the are by inclosingchamber or envelop, for the reason that the mercury are is somewhatunstable, and also because of the extremely poisonous vapors which itproduces. I have further shown that the color-modifying substances whichfulfil the necessary conditions, as for exam ple, potassium, sodium,lithium,rliubidiuunA indium and tliallium, vigorously attack thetransparent envelop, which, for example, may be constituted. of the besthard glass, and form :onlthe inside thereof a black deposit whichdestro-ys the usefulness of the lamp in a very short time, so that thelamp eau scarcely be said to be operative if the color-modi tyingsubstances are introduced in the simple manner thus far described. In mysaid former application I have set forth at considerable length a methodof overcoming this diticulty, which consists in causing thecolormodifying substances to exist in the arc in an ionized state, whichmay be brought about, as described in said application, by introducingthem, not in their natural condition, but rather as anhydrous iodids, orother halogen salts, with or without a neutral or diluent substance forthe purpose of reducing the effect of the color-modifying substancesupon the are. Ina certain other application for Letters Patent, April21,

substances have, it is true, some chemical` action upon the glass, butthe continual combination land recombination which takes place 1s suchas to preserve the translucency of the envelop, for the reason that thesalts` formed by such action are translucent in their nature, and theinner surface of the envelop is not blackened, but merely given anagreeable frosted appearance.-

My present application sets forth and claims certain improvements upon"the methods and apparatus described in the above- `mentionedapplications.

O ne feature of my present invention is the reduction of the potentialnecessary `to start the arc by the use of a rarefied atmosphere ofhydrogen or other material of lower dielectric strength than air, as forexample helion or argon, by which I am able to very greatly reduce theinitial voltage necessary for the starting of the lamp.

Further, I find that the action of the halo-- paratively speaking,whereas they should,

for best results, be uniformly distributed over the terminal in orderthat the are may at all times run through a layer of colormodifyingsubstance. The silicates above discussed do notshare this disadvantage,

but they are all open to the objection thatv their action takes place ata temperature vslightly higher than that of the action of the iodids.

Further, I nd that the iodids actually tend to emphasize and bring outthe color of the modifying substances, imparting awarmer tinge to thelight from the lamp. Therefore in lamps constructed in accordance withmy present invention, I wholly inclose the mercury or other lightgivingsubstance in a hermetically-sealed glass vessel filled, say, withhydrogen, and exhausted to a fairly high vacuum, measured for example byonemillimeter of mercury on the ordinary scale or less. Further, Iprovide for an excessof iodin in the colormodifying substances, by theaddition ofV free iodin or of iodid of mercury, or in someotherequivalent manner.

My present invention further comprises a new means for the initialstarting of the lamp, which will be fully described land claimed below,as well as an automatic arrangement whereby the length of theo arc willbe regulated and maintained within definite limits by the pressuregenerated by the arc itself.

The drawings accompanying this specification represent a simple form oflamp embodying certain features of my present invention.

and the surfaces of the electrodes are cov-V' ered with acolor-modifying substance, in accordance with the principles above setforth. In this particular case we may assume that it is desired toproduce whiteV light, in which case the color-modifying substance may beconstituted of a mixturel of the iodids of lithium and sodium, orlithium, sodium and potassium, which mixture is prepared by heatingthese iodids, the lithium iodid preponderating, in an atmosphere ofhydrogen under reduced pressure with the addition of some free iodinand` with the exclusion of air. To this mixture -of oidids may be addeda diluent substance such as fiuorid of calcium. This type of lamp ispreferably included ."fn/,afconstantcurrent circuit, in series. Itis'well to warm minals nearly to the boiling point of the mercury, bytheapplication of a spirit lamp or other source of heat. When this resulthas been achieved, the lamp is included in the constant-current circuit,alternating or direct, by any suitable switching apparatus, whereuponthe arc strilies across from one electrode to the other land fills thewhole tube, or the central portion of the tube, according to the degreeof thevacuum, with a beautiful white light. The mercury furnishes theviolet, blue, green and yellow lines of the spectrum, while the orangeand red lines are furnished by the color-modifythe lamp, andparticularly to raise the terloo ing substances sodium and lithium. Asthe arc plays over the surface of the mercury, it is continuously takingup small quantities ofthe lithium and sodium iodids, which disassociatein the arc, allowing the metallic pieces to vibrate under theelectrostatic stress, or otherwise asthe case may be, while thedisassociated atoms of iodin continuously stand guard, as it'were, overthe atoms of sodium and lithium, and preventl them from attacking theglass. This is the result of the fact that the metallic substances existin the arc in a state in which their natural aiiinity for the glass isto a certain extent satisfied, as it were, bythe tendency of the iodinatoms to be combined with them. Thus the 4glass is protected, and theadditional free iodin above mentioned tends to help the color-modifyingsubstances to fulfil their functions, which I attribute to the fact thatthe excess increases the volatility of the lithium and potassium.

By increasing the amount of any one of the color-modifying substances,and by suitiso ' ably choosing said substances in laccordance with theirknown arc spectra, the light may be given any desired color.

In conclusion, Iwillstate that although V by Letters Patent of theUnited States, is,

1 VU.'Ihemethod of producing 'light of any .desired color or combinationAof colors,

which consists in drawing `an arc from a terminal vaporizable at a lowtemperature in a suitable envelop, introducinga c0lormodifyingsubstanceto the arc and maintainin it in an ionized 'state bytheaddiltion 0 a protecting substance, andincreasing the action ofthe-color-modifying subl20 stance by the introduction-of an excess ofthe protecting substance.

2. The method of modifying the color of an arc light and protecting theinclosure in which the`same is contained, which consists 2'5 invintroducing vaporous colormodifying substances ina form in which theirchemical activity withfreference to the envelop is neutralized, andprotecting the modifying substances from -the action, of moisture or of30 the atmosphere.

In witnesswhereof I have hereunto set my hand this 2.7 th day of April,1.900.

y le CHARLES P. STEINMETZ. Witnesses: p l

BENJAMIN B; HULL, ALEX F. MACDONALD.

